In a fluid pressure cylinder which drives a reciprocating rod, that is, a piston rod by hydraulic pressure or pneumatic pressure, when the reciprocating rod is stopped at a stroke end of the reciprocating rod, an impact force is applied to the reciprocating rod and a moving member such as a member to be driven by the reciprocating rod. To decrease the impact force, a buffer such as a resin-made damper, air cushion, hydraulic cushion, shock absorber is used so that the moving member collides with a member on a fixing side through the buffer.
For example, when an electronic component or jig is carried with a reciprocating rod of a pneumatic cylinder, unless any buffer is provided to the pneumatic cylinder, a product to be carried such as the electronic component, namely, a member to be driven receives the impact force at the stroke end of the reciprocating rod. As a result, not only the product to be carried is moved to an unexpected place or damaged or dropped but also a large vibration occurs, thereby shortening a lifetime of the pneumatic cylinder or an electronic-component manufacturing apparatus including the same. To decrease such an impact force at the stroke end, the aforementioned buffer is provided to the pneumatic cylinder. If carrying speed is reduced without providing the buffer in order to prevent the product to be carried from dropping, an operating ratio of the electronic-component manufacturing apparatus drops. If a member for securely fixing the product to be carried to the moving member is used, an entire structure of the apparatus is made large.
The shock absorber as a buffer is often used to stop the product to be carried moving at high speed or to stop movement of a heavy product to be carried. The shock absorber includes one of a type of making a rod protrude from an end portion of a cylindrical case (see Patent Document 1: Japanese Utility Model Laid-Open Publication No. 61-55530).
To use the shock absorber of such a type to absorb the impact force at the stroke end of the reciprocating rod driven by the pneumatic cylinder, the shock absorber is attached to a side face of a cylinder main body while a stopper with which the rod of the shock absorber collides is attached to the reciprocating rod.
FIG. 10 is a perspective view showing a conventional slide table type pneumatic cylinder, which includes a cylinder main body 1 and a reciprocating table 3 mounted reciprocably to a guide rail 2 provided to the body. As shown in FIG. 10, in a pneumatic cylinder in which a reciprocating rod 4 provided to the cylinder main body 1 is connected to the reciprocating table 3 through a linking member 3a so as to drive the reciprocating table 3 by the reciprocating rod 4, shock absorbers 5a and 5b are attached to the cylinder main body 1 through brackets 6a and 6b in order to absorb the impact force at the stroke end of the reciprocating rod 4 or reciprocating table 3, and a stopper 8 with which the rods 7a and 7b of the shock absorbers 5a and 5b collide is attached to the reciprocating table 3.
Also, if the shock absorbers 5a and 5b are attached to the reciprocating table 3, the stopper with which the rods 7a and 7b of the shock absorbers 5a and 5b collide is to be attached to the cylinder main body 1. In any case, the rods 7a and 7b absorb the impact force of the reciprocating table 3 while moving and retracting into cylindrical cases of the shock absorbers 5a and 5b. 
In the shock absorber of such a type, the cylindrical case is filled with fluid such as silicone oil, and a spring or the like for returning, to an original position, the rod moved and retracted at a time of collision is incorporated in the cylindrical case.
In the case where a conventional shock absorber is used to absorb the impact force of the reciprocating unit such as the pneumatic cylinder, even if the shock absorber is attached to the cylinder main body or to the reciprocating table in an above-mentioned manner, the shock absorber is attached apart from an axial center of the cylinder main body. For this reason, the shock absorber has been attached at a position protruding from a side face or upper face of the reciprocating table or at a side face of the pneumatic cylinder.
Thus, since the shock absorber absorbs the impact force at a position offset from the axial center of the pneumatic cylinder, a bending moment is applied to the reciprocating table and the reciprocating rod in absorbing the impact force and so the bending moment is applied also to a guide rail which supports the reciprocating table. Accordingly, strength of the cylinder main body, reciprocating table and guide rail needs to be increased.
As shown in FIG. 10, if the shock absorbers 5a and 5b are attached to the cylinder main body 1, the stopper 8 which collides with the rods 7a and 7b needs to be attached to the reciprocating table 3. If the shock absorbers 5a and 5b are attached to the reciprocating table 3, the stopper 8 which collides with the rods 7a and 7b needs to be attached to the cylinder main body 1. Thus, the number of parts constituting the pneumatic cylinder increases and concurrently a size of the apparatus is made large. Further, if the stopper is attached to the reciprocating rod and the shock absorber is attached to an outer face of the cylinder main body, a rotation stopper for the reciprocating rod needs to be provided to the cylinder main body so that the reciprocating rod collides with the rods of the shock absorber.
Meanwhile, in order to dispose the shock absorber coaxially with the reciprocating rod so that no bending moment is applied to the reciprocating rod of the pneumatic cylinder at a time of absorbing the impact force, it is necessary to attach a fixing jig such as a bracket to the cylinder main body and attach the shock absorber to the cylinder main body through the fixing jig. Therefore, since the fixing jig protrudes from a periphery of the cylinder main body, space efficiency in the cylinder main body is bad.
An object of the present invention is to attach a shock absorber coaxially to a reciprocating rod driven by a reciprocating unit such as a pneumatic cylinder so as to apply no bending moment to the reciprocating rod in absorbing an impact force.
Another object of the present invention is to directly attach the shock absorber to the reciprocating rod to eliminate a fixing jig for attaching the shock absorber or a stopper which collides with the shock absorber, thereby reducing a manufacture cost of the reciprocating unit.
Still another object of the present invention is to directly attach the shock absorber to the reciprocating rod to save a space on a periphery of the reciprocating unit.
Yet still another object of the present invention is to be capable of adjusting a stroke of the reciprocating rod by adjusting an axial attaching position of the shock absorber with respect to the reciprocating rod.